A navigation system for use in a vehicle is equipped with a display device which is used when a route is determined, or the display device is opened automatically or according to driver's request when the vehicle is guided by the navigation system. When a map for determining an optimum route is to be displayed, conditions under which the route is to be set are entered, and searching of the route is started. Then, a detailed map containing the route is displayed. This map is hereinafter referred to as the route search map. When the search is completed, a whole route map, or a wide-area map, is displayed in a form which permits the driver to clearly discern the whole route. The driver can visually and aurally recognize from the whole route map only the route going from the present location to the destination. Subsequently, the driver depresses a guide start button to initiate guidance by means of the navigation system.
As a result of the search, the driver might find that he or she is well acquainted with the displayed route up to an intermediate point. The driver does require guidance along such a familiar route; it suffices to guide the driver only along a further route unknown to him or her. For example, where the route contains a tollway such as an expressway, if the driver is well acquainted with the route up to an interchange with ramps, and if this familiar route is utilized, then the driver is able to drive comfortably. With the conventional navigation system, however, the driver is guided along the whole route even if the driver knows the route up to the utilized interchange. Furthermore, only a whole route map is displayed. Therefore, it is difficult for the driver to understand landmarks along the route to the destination.